The invention relates to a sweeping machine comprising a sweeping brush that is capable of being driven in rotation, a debris container and a suction fan for suctioning dust-laden air, and at least one filter arranged in the flow path between the sweeping brush and the suction fan, for separating particles of dust and dirt from the suctioned air, wherein the filter is in flow communication with the suction fan by way of a suction conduit and is in flow communication with a pressure vessel by way of an external air conduit and at least one external air valve and, for filter cleaning, is capable of having applied thereto external air that is stored in the pressure vessel and is under positive pressure.
By using such sweeping machines, a ground surface can be swept, with coarse debris being transferred into the debris container by the sweeping brush, which is capable of being driven in rotation. Performing the sweeping operation on a dry ground surface often causes considerable amounts of dust to be generated. To counteract this, the sweeping machine has a suction fan which is in flow communication with the sweeping brush so that dust-laden air can be suctioned, whereby the generation of dust can be reduced. On its way from the sweeping brush to the suction fan, the drawn air passes through at least one filter where dust and dirt particles entrained in the air can be separated.
During operation of the sweeping machine, dust and dirt particles are increasingly deposited on the at least one filter's dirty side, which faces towards the sweeping brush, and as a result of this the filter offers increasing resistance to flow. Therefore, it is necessary to clean the filter from time to time. For this purpose, WO 2009/132757 A1 proposes a manual filter cleaning device comprising a slider which can be displaced by the user along the dirty side of the filter. With the aid of said slider, dust and dirt particles adhering to the dirty side of the filter can be wiped off.
Document DE 34 06 816 A1 discloses a sweeping machine in which the filter is configured in the form of a cylindrical filter cartridge. An external air supply tube extends into the filter cartridge on a clean side thereof so that via the external air supply tube, which has a multiplicity of nozzle-like openings, external air under pressure can be supplied to the clean side of the filter. The external air supply tube is in flow communication with a connection piece by way of a hose conduit, and said connection piece is capable of being connected to a source of compressed air. This provides the possibility of applying external air under pressure to the clean side of the filter by way of the compressed air supply tube. The external air can pass through the filter cartridge in the reverse direction with respect to the direction of flow during normal sweeping operation, whereby dust and dirt particles adhered to the dirty side of the filter cartridge can be dislodged.
Also, sweeping machines are known in which, in lieu of an external air supply tube which extends axially into a filter cartridge and has a multiplicity of lateral openings, an external air supply nozzle is used which is arranged in alignment with the longitudinal axis of the filter cartridge, at a distance to the clean side thereof. By way of the external air supply nozzle, external air under positive pressure can flow into the cylindrical filter cartridge from the clean side thereof. Provision may be made for the sweeping machine to have a multiplicity of filter cartridges which are arranged parallel to one another and each of which has an external air supply nozzle associated with it. The external air supply nozzles are in flow communication with a pressure vessel by way of an external air conduit, said pressure vessel holding a store of external air under positive pressure. Such a sweeping machine is described for example in document DE 26 29 967 A1 A similar sweeping machine is disclosed in U.S. Pat. No. 4,756,727 A.
In order for the external air flowing from the external air supply nozzle to the filter cartridge to cover as large an area as possible on the clean side thereof, U.S. Pat. No. 4,452,616 proposes the use of a diffuser arranged between the external air supply nozzle and the filter cartridge. A similar configuration is described in U.S. Pat. No. 3,798,878.
In order to achieve as effective a filter cleaning action as possible, U.S. Pat. No. 4,486,201 proposes, in addition to the use of an external air supply nozzle that is arranged in alignment with the longitudinal axis of a filter cartridge and applies external air under positive pressure to the clean side of the filter cartridge, the use of further external air supply nozzles that direct external air at the dirty side of the filter cartridge, wherein the external air is routed axially along the dirty side of the filter cartridge in order to enhance the release of dust and dirt particles from the dirty side of the filter.
A disadvantage associated with the known sweeping machines is that an effective filter cleaning operation is only ensured when a considerable amount of external air is passed through the filter. This large amount of external air must subsequently be extracted again by the suction fan within a short interval of time, because otherwise there is a risk of the external air escaping from the sweeping machine in the area of the sweeping brush, thereby increasing the generation of dust when sweeping is being performed on a dry ground surface. A further disadvantage is that the external air has to be supplied under considerable positive pressure to the filters. Thus, for example, DE 26 29 967 A1 proposes a pressure greater than 7 bar for the external air. Such a level of positive pressure requires additional safety precautions to be taken in order to prevent hazard to the user of the sweeping machine.
It is therefore an object of the present invention to improve a sweeping machine of the kind mentioned at the outset such that the at least one filter can be cleaned effectively with as small an amount of external air as possible and with said external air being at as low a positive pressure as possible.